A large portion of oil and reserves now undergoing recovery can be characterized as heavy oil or bitumen, typically containing high levels of maltene and asphaltene fractions. Because heavy oils are forming a larger proportion of production volumes, their conversion into lower boiling and more valuable fractions such as gasoline, kerosene and road diesel, is progressively forming a greater part of the petroleum refining process.
Considerable process technology already exists for upgrading heavy crudes, bitumens, and coal liquids. Among those broad categories of known heavy oil primary upgrading processes are carbon rejection process such as catalytic cracking, thermal cracking e.g. coking, demetallization processes, hydrogen addition processes such as hydrocracking and gasification or combustion processes. The presence of high levels of metal contaminants in these fractions creates problems in both catalytic and non-catalytic refining processes. Catalytic processes, whether of the hydrogen addition or carbon rejection type often require the use of large quantities of solid catalysts which are subject to reduced throughput and high catalyst replacement costs resulting from the catalyst deactivation when processing heavy oils when the contaminants can migrate onto the catalyst at high temperatures. Deactivation usually results from the deposition of contaminants onto the surfaces of the catalysts from the feed; contaminants typically include metal compounds, high molecular weight refractory compounds (or coke derived therefrom), or sulfur or nitrogen containing heterocyclic compounds. Depending on the identity of these contaminants, they may react with catalyst components under certain conditions to form low melting eutectic compositions which can either sinter molecular sieves, zeolites, or other high surface area catalyst supports components or block catalyst pores. In either case, catalyst effectiveness is significantly reduced. In addition, the presence of catalytic metals may have deleterious effects upon the process itself; in catalytic cracking, for example, high levels of nickel or vanadium in the feed may effectuate excessive gas and coke formation in the cracker. Finally, if these metals are carried through to the products, adverse consequences may result from their use, for instance, vanadium in fuel oils is apt to lead to the formation of sulfur oxides in the atmosphere and “acid rain”.
In thermal carbon rejection processes, the presence of high levels of metal contaminants may lead to the generation of hard, adherent fouling deposits on the walls of equipment used in the processing, especially furnaces and heat exchangers. Asphaltenes and some resin fractions typically contain significant quantities of these contaminants and so, even though asphaltenes may comprise only 10% to 15% of some heavy oil feedstocks, they disproportionally contribute to the fouling of refinery equipment or the deactivation of solid catalysts. The predominant metallic poisons in heavy oils, resids and bitumens are nickel and vanadium metalloporphyrins which should be removed to the extent possible before these materials enter thermal or catalytic upgrading processes. Various types of demetallization processes are known in the refining industry including solvent extraction with both hydrocarbon and aqueous extractants as well as catalytic hydrogenative processes. Solvent deasphalting using light paraffinic solvents such as propane and butane are effective to a certain extent for demetallization since they remove a portion of the metalloporphyrins in the asphaltene fraction which is precipitated by the paraffin.
U.S. Pat. No. 6,007,705 (Greaney) discloses one example of an aqueous extraction process for demetallizing by contacting a metals-containing petroleum feed in the presence of an aqueous base selected from Group IA and IIA hydroxides and carbonates and ammonium hydroxide and carbonate together with an oxygen containing gas and a phase transfer agent at a temperature of up to 180° C.
Combined oxidative/extraction techniques have also been explored as described by Gould, “Oxidative demetallization of petroleum asphaltenes and residua”, Fuel, vol. 59, pp. 773-736 (October 1980): asphaltenes and vacuum residuum were treated with oxidizing agents in aqueous solutions, including peroxyacetic acid, which exhibited high demetallization activity coupled with the ability to remove or destroy petroporphyrins.